Pushed a patch to catch when the tool from docbook to mack conversion is not available and just print an info message. I think this should do it for now, if one wants to start generating man pages, can do it by installing the tool.
I will close this issue and if one wants to package man pages for modules' readme, open a feature request. To my knowledge, so far they were never packaged. If some new issues after the patch, just reopen.